Active matrix display devices having a plurality of pixels arranged in a matrix have been in widespread use. In general, the pixel includes a transistor, a scan line electrically connected to a gate of the transistor, a signal line electrically connected to one of a source and a drain of the transistor. The transistor is turned on by controlling a potential of the scan line, and a potential of the signal line is controlled so as to be a data signal to the pixel. Accordingly, a desired data signal can be supplied to a desired pixel. The display device displays images by performing such an operation successively to each pixel. At present, display of a display device is generally written 60 times per second (60 Hz). That is, a data signal is generally input (rewritten) once about every 0.0167 seconds.
In recent years, concern for the global environment has been increased and development of low-power-consumption display devices has been attracting attention. For example, a technique in which power consumption of a display device is reduced by decreasing rewriting frequency of display of the display device is disclosed in Patent Document 1. A specific structure of the display device disclosed in Patent Document 1 is described below.
In the display device disclosed in Patent Document 1, a scanning period in which one screen is scanned and a break period which follows the scanning period and is longer than the scanning period are set. In the Patent Document 1, the following technique is disclosed: in the break period, a potential of a scan line is fixed to a non-selection signal, and a potential of a signal line is (1) set at a fixed potential, (2) set at a fixed potential and then brought into a floating state, or (3) used as an alternating-current driving signal which is equal to or lower than the frequency of a data signal. Thus, power consumption in accordance with variation in the potential of the signal line in the break period is reduced. In addition, in the case where the potential of the signal line is used as an alternating-current driving signal which is equal to or lower than the frequency of the data signal (in the case of (3)) in the break period, variation in a potential of the pixel electrode caused by capacitive coupling between the signal line and the pixel electrode can be almost constant in the scanning period and the break period.